Disk drives are digital data storage devices that may allow host computers to store and retrieve large amounts of data in a fast and efficient manner. A typical disk drive may include a plurality of magnetic recording disks, which may be mounted to a rotatable hub of a spindle motor and rotated at a high speed. An array of read/write heads may be disposed adjacent to data storage surfaces of the disks to transfer data between the disks and a host computer. The heads can be radially positioned over the disks by a rotary actuator and a closed loop servo system, and can fly in close proximity to the surfaces of the disks upon air bearings. The heads each typically contain a separate read element and write element.
Higher data storage density on the disks may be obtained by reading and writing data on narrower tracks on the disks, and/or by maintaining narrower flying height gaps between the heads and the data storage surfaces. The flying height of a head can vary in response to air density changes in the disk drive and/or in response to head temperature variations that can affect the distance that the tip of the head protrudes therefrom (i.e., pole tip protrusion). Accordingly, some disk drives may controllably heat the head using a heater element to vary the flying height of the head. More particularly, dynamically controlled fly height or Fly Height Adjust (FHA) may be achieved using an actuation coil built into the head. When power is applied to the coil, the head may protrude towards the disk. As such, by adjusting the power applied to the heater element, a fly height/spacing between the head and the disk surface can be maintained in a variety of changing environmental conditions, for example, due to changes in temperature, barometric pressure, etc.
Maintaining the head flying height within a desired or acceptable range may become increasingly more difficult as that range is reduced to obtain higher data storage densities. Operation outside the acceptable range may result in an unacceptable read/write bit error rate and/or undesirable contact between a head and a data storage surface and potential loss of data and/or damage to the data storage surface. For example, in cases where a head inadvertently contacts the disk during normal drive operation, burnishing or degrading of a protective overcoat on an air bearing surface of the head may result. The loss of the overcoat may result in increased susceptibility to corrosion and/or shortening of the head life. Also, as the head's air bearing surface may be used to build pressure to lift the head from the disk surface during normal drive operation, burnishing of the air bearing surface may alter the spacing between the head and the disk surface and/or may result in a “softer” air bearing.